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To investigate the changes of osteopontin (OPN) mRNA expression induced by angiotensin II (AngII) in RAW264.7 macrophages, and to determine the role of p38 mitogen-activated protein kinase (p38MAPK) signaling in up-regulation of OPN mRNA expression.RT-PCR was used for examining the OPN mRNA expression, and the phosphorylation of p38MAPK and activating transcription factor2 (ATF2) was detected by Western blot.(1) AngII (1 micromol/L) enhanced the expression of OPN mRNA in RAW264.7 macrophages with time-dependent, including 0.9 fold, 2.3 folds and 2.4 folds up-regulation at 6, 12, 24 h, respectively (all P0.01), whereas there was no significant change in negative control at 0 h and 24 h, suggesting that the mRNA expression of OPN is inducible. (2) Following excitation by Ang II in vitro, there was substantial up-regulation of OPN mRNA expression in RAW264.7 macrophages with dose-dependent; with a dose of 1 micromol/L incubated for 12 h, Ang II increased the OPN mRNA expression by 2.6 folds (P0.01). (3) Pre-treatment with SB202190 (5 micromol/L) for 30 min in RAW264.7 macrophages before AngII (1 micromol/L) used, the expression of OPN mRNA was inhibited by 61.7% (P0.01); but no marked inhibition had happened at the time of treatment with both SB202190 (5 micromol/L) and Ang II (1 micromol/L) added at the same time and with SB202190 (5 micromol/L) for 120 min after Ang II (1 micromol/L) used. (4) Pre-treatment with SB202190 (1, 5, 10 micromol/L) for 30 min in RAW264.7 macrophages before Ang II (1 micromol/L) used, the expression of OPN mRNA was decreased by 43.4%, 63.0% and 65.5%, respectively (all P0.01). (5) There was a maximal expression of p38MAPK phosphorylation at 15 approximately 30 min induced by Ang II (1 micromol/L) in RAW264.7 macrophages, and the maximal expression of phosphorylated ATF2 was at 30 approximately 45 min. (6) Pre-treatment with SB202190 (1, 5 micromol/L) for 30 min in RAW264.7 macrophages before Ang II (1 micromol/L) used, the expression of p38MAPK phosphorylation was inhibited markedly with dose-dependent, and the phosphorylation of p38MAPK was decreased by 61.7% (P0.01) after the SB202190 (5 micromol/L) was used.Angiotensin II may up-regulate osteopontin mRNA expression of RAW264.7 macrophages via p38MAPK signaling.